Magnetic control devices



Feb. 19, 1957 P. H. BRIGGS MAGNETIC CONTROL DEVICES Filed Feb. 9, 1953 -19 T fly .llzzvelz/ ZZ.Z31 ZL 5 2 fitiil w.

United States Patent M MAGNETIC CONTROL DEVICES Philip H. Briggs, Wythenshawe, Manchester, England, as-

signor t0 Robertshaw-Fulton Controls Company, Greensburg, Pa.

Application February 9, 1953, Serial No. 335,897 1 Claim. (Cl. 323-40 This invention relates to magnetic devices, and has for its object to provide means for indicating, controlling or recording variations in voltages or resistances or quantities on which voltages or resistances can be made to depend, such means being economical as regards the amount of magnetic material used.

According to the invention, the indicating, controlling or recording means comprises a core having a closed magnetic circuit and a center leg across the circuit, and windings on the outer limbs of the core connected in series across a voltage supply, and means associated with the windings for controlling the voltages developed therein, and if required mean for indicating or recording such voltages.

For the purpose of obtaining a constant voltage irrespective of fluctuations in the supply voltage, a part or all of one winding may have connected across it a resistance or impedance which is variable in accordance with the voltage developed across the other winding or a suitably proportioned separate or auto transformer winding associated therewith, such voltage being the output voltage. A convenient arrangement is one which has a carbon pile resistance, the pressure on which is varied by a voltagesensitive electro-magnetic device.

By this means the output voltage can be automatically regulated over a wide range of variation of the supply voltage, and only one transformer is required which need not be of large dimensions, although the core should be of sufiicient size to avoid saturation occurring.

In another arrangement in accordance with the invention, impedances are connected across the windings, one or both of which are variable. For example in a particular application there is an impedance across one winding, and a thermionic tube or tubes controlled by an error detecting device across the other winding. A further winding is provided on the bridge across the core, and the phase and magnitude of the current induced in such winding depends on the impedance across the main windings, and in the example referred to it is zero when the tube impedance has a given value.

It is further possible to provide additional windings in conjunction with the main windings so as to obtain voltages proportional to the voltages therein, and to connect such windings together in the same or in opposite senses to obtain either the sum or the difference of such proportional voltages, as required.

A further possibility is to provide a winding in conjunction with one of the main windings, with the object of modifying the impedance of that main winding to obtain an indication of an impedance in series with the additional winding.

Referring to the accompanying drawings:

Figure 1 shows a voltage regulating device according to the invention.

Figures 2 and 3 are diagrams explaining the operation of the device of Figure 1.

Figures 4 and 5. show two types of indicating appliance according to the invention.

2,782,363 Patented Feb. 19, 1957 Referring to Figure 1, the voltage regulating device has a closed magnetic core with two outer legs 1, 2 and a center leg 3. Secured to the legs 1, 2 are two windings 4, 5 respectively. The winding 5 and part of the winding 4 are connected in series in magnetic assistance and energised by an A. C. supply connected at 6. The winding 4 is connected to output terminals 7, and a voltage-sensitive electro-nagnetic device 8 such as a voltage meter is connected across it, and has its pointer mechanically coupled to a carbon pile resistance 9 connected across a part of the winding 5. With this arrangement the output voltage obtained at the terminals 7 is constant irrespective of variations in the input voltage applied at 6. The variable resistance 9 immediately responds to and compensates for any variation in the output voltage by restoring the voltage to the desired value.

The operation of the device will be more clearly understood by reference to the simple electric circuit of Figure 2. In Figure 2, a variable voltage is applied at 6, and is controlled by a resistance 9 actuated by the movement of the pointer in the voltmeter 8 connected across the output terminals '7. The device 3 actuates the resistance 9 so as to reduce its resistance if the output voltage falls, and vice versa.

If the output voltage so obtained, taking into consideration the variations in the supply voltage, may be too low, an auto-transformer 4. is inserted as shown in Figure 3.

1 A convenient type of resistance 9 is a carbon pile regulator, which can handle only a limited amount of voltage variation, although the current that may be passed is not a limiting factor. Consequently a further auto transformer 5 is provided so that a major portion of the voltage variation is compensated for in the autotransformer 5 and the carbon pile resistance 9 only operates to correct for the liner adjustments of the voltage variation, the maximum voltage developed in the resistance 9 may be kept within the appropriate limits. The circuit shown in Figure 3 differs from that shown in Figure 2 by the addition of the autotransformers 4 and 5 shunted across the voltmeter 8 and resistance 9 respectively.

The two auto transformers 4 and 5 are mounted on a single core as in Figure 1, whereby a saving of iron is achieved, since the center leg 3 carries only the differential flux of the two magnetic circuits. The auto transformer 4 enables an output voltage to be selected independently of the source. Similarly, the auto transformer 5 enables the resistance 9 to be selected without the usual limitations as to ohmic value and current carrying capacity. It will be apparent that this arrangement of two auto transformers on a common magnetic circuit provides an efiicient voltage regulating device.

Figure 4 shows an arrangement suitable for operating a servo mechanism in accordance with the movements or indications of an error or other detecting device.

The arrangement includes a closed magnetic core having three legs it, 2 and 3 and windings 4, 5 on the legs 1, 2, respectively, connected in series assistance, with a resistance 9 across the winding 5, and supplied with power at 6, as in Figure l. Across the winding 4, is connected a thermionic tube it the input to which is derived from an amplifier l1 controlled by an error detecting device 12. The device 12 may for example be a capacitative device having two electrodes forming a condenser one of which is moved, so as tochange the capacity, by a change in a voltage, in the level of a liquid or in some other quantity, the other electrode then being moved to restore the original value of the capacity, by a split phase servo motor 13 which may also operate recording, indicatmg or controlling equipment. 0n the center leg 3, there is a winding 14 connected to the driving winding of the servo motor 13. The windings 15, 16 are connected on series on the legs 1, 2, respectively, and provide a voltage proportional to the supply voltage, for supplying the filament of the tube 10 and the reference winding of the motor 13. Alternatively, a separate transformer could be used for this purpose.

In normal conditions, since the resistance 9 is in the anode circuit of the tubelt) the conduction of the tube 10 matches that of the resistance 9 and the magnetic fluxes linked by the windings 4 and 5 are equal and there is no flux differential in the center leg 3, and consequently in the center winding 14. If the device 12 shows a variation in the quantity being controlled, it varies the output of the amplifier 11 and consequently varies the conduction of the tube 10 in a corresponding direction. This re sults in a flux in the leg 3, and a current in the winding 14, corresponding in magnitude and direction to the variation at 12, whereby the servo motor 13 is driven in the appropriate direction, and continues to run until the variation is removed, and the circuit is again balanced and in a normal condition.

The device 12 could comprise for example a volt meter movement having the usual pointer carrying a capacitative vane, and a movable arm carrying a second vane. When the applied voltage varies, the pointer is deflected and the servo motor drives the arm until its vane is again spaced its original distance from the pointer vane, and at the same time drives an arm carrying a recording pen to an extent corresponding to the deflection of the pointer.

If for manufacturing reasons it were not desired to provide windings on all three legs, the winding 14 could be replaced by windings 17, 18 on the legs It, 2 connected in series opposition, as shown in broken lines.

Figure 5 shows a magnetic appliance for indicating values of resistances or quantities equivalent thereto. As in Figures 1 and 4, the core has legs 1, 2, 3 and windings 4, 5 connected in series assistance to power supply terminals 6. A measuring instrument 19 is connected across the winding 4, and a coil 20 connected in series with a variable resistance 21 is linked with magnetic circuit of the winding 5. Any variation in the resistance 21 causes a corresponding deflection of the meter 19. Such variation could be produced by an instrument measuring an unknown quantity, not necessarily an electrical quantity and actuating the variable resistance accordingly, or by a change in the resistance of a conductor due to a change of temperature, or the like.

In order to obtain increased sensitivity, the meter 19 could be connected as shown in broken lines in a bridge circuit, between the junction of the windings 4, 5 and the center of an induction 22 connected across the terminals 6.

What I claim is:

In a voltage regulating device having a source of alternating voltage, the combination comprising a closed magnetic core having two outer legs and a center leg, an inductance coil wound on each of said outer legs and defining a pair of auto transformers each having an input and an output portion, circuit means for connecting said input portions of said transformers in series across the source, a pair of output terminals for the regulating device connected across said output portion of one of said transformers, a variable resistance element connected across said output portion of said other transformer, a voltage sensitive device coupled to said output portion of said one transformer and being mechanically coupled to said variable resistance element, said element being responsive to any voltage variation of the source for compensating therefor whereby the desired voltage value is restored.

References Cited in the file of this patent UNITED STATES PATENTS l,8l7,334 Anderson Aug. 4, 193l 1,909,053 George May 16, 1933 2,134,517 Jones Oct. 25, 1938 2,573,388 Billing Feb. 7, 1950 

